Dynamic inferred coupling estimation

ABSTRACT

Systems, methods and apparatus for providing a wireless charging device are disclosed. A method for operating the wireless charging device includes transmitting a first pulse through each of a plurality of charging circuits, determining peak voltage at nodes in the plurality of charging circuits, each node coupling a transmitting coil to a capacitor in one charging circuit in the plurality of charging circuits, the peak voltage at each node being responsive to the first pulse and indicative of a coupling coefficient with a receiving coil in a chargeable device, determining that a minimum peak voltage responsive to the first pulse is associated with a first charging circuit in the plurality of charging circuits, and providing a first charging current to the first charging circuit.

PRIORITY CLAIM

This application claims priority to and the benefit of provisionalpatent application No. 62/877,831 filed in the United States PatentOffice on Jul. 23, 2019, and the entire content of this provisionalapplication is incorporated herein by reference as if fully set forthbelow in their entirety and for all applicable purposes.

TECHNICAL FIELD

The present invention relates generally to wireless charging ofbatteries, including batteries in mobile computing devices, and moreparticularly to detection of device location prior to a chargingoperation and relocations during the charging operation.

BACKGROUND

Wireless charging systems have been deployed to enable certain types ofdevices to charge internal batteries without the use of a physicalcharging connection. Devices that can take advantage of wirelesscharging include mobile processing and/or communication devices.Standards, such as the Qi standard defined by the Wireless PowerConsortium enable devices manufactured by a first supplier to bewirelessly charged using a charger manufactured by a second supplier.Standards for wireless charging are optimized for relatively simpleconfigurations of devices and tend to provide basic chargingcapabilities.

Improvements in wireless charging capabilities are required to supportcontinually increasing complexity of mobile devices and changing formfactors. For example, there is a need for a faster, lower powerdetection techniques that can locate a chargeable device placed on acharging surface of a charging device, and relocation of the chargeabledevice during a charging operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a charging cell that may be employed toprovide a charging surface in accordance with certain aspects disclosedherein.

FIG. 2 illustrates the arrangement of power transfer areas provided by acharging surface that employs multiple layers of charging cellsconfigured in accordance with certain aspects disclosed herein.

FIG. 3 illustrates a wireless transmitter that may be provided in acharger base station in accordance with certain aspects disclosedherein.

FIG. 4 illustrates a first example of a response to a passive ping inaccordance with certain aspects disclosed herein.

FIG. 5 illustrates a second example of a response to a passive ping inaccordance with certain aspects disclosed herein.

FIG. 6 illustrates examples of observed differences in responses to apassive ping in accordance with certain aspects disclosed herein.

FIG. 7 is a flowchart that illustrates a method involving passive pingimplemented in a wireless charging device adapted in accordance withcertain aspects disclosed herein.

FIG. 8 illustrates frequency response of a resonant circuit to a pingprovided at the resonant frequency of the resonant circuit.

FIG. 9 illustrates frequency response of a resonant circuit illustratingthe effect of a ping provided at a frequency greater than the resonantfrequency of the resonant circuit in accordance with certain aspectsdisclosed herein.

FIG. 10 illustrates an example of coupling in a wireless charging systemthat includes multiple charging coils in accordance with certain aspectsdisclosed herein.

FIG. 11 illustrates a charging environment in which a receiving deviceand a charging device exchange messages including digital pings andreceived power reports.

FIG. 12 illustrates the effect of coupling on voltage measured at a nodeof the transmitter in a wireless charging system in accordance withcertain aspects disclosed herein.

FIG. 13 illustrates effects of placement and movement of chargeabledevices in accordance with certain aspects disclosed herein.

FIG. 14 illustrates an example of removal of a wireless charging systemthat can concurrently charge multiple devices in accordance with certainaspects disclosed herein.

FIG. 15 illustrates an example of removal of a charging device that mayresult in a wireless power transmitting system detecting a phantomreceiver.

FIG. 16 is a flowchart illustrating phantom receiver detection inaccordance with certain aspects disclosed herein.

FIG. 17 illustrates one example of an apparatus employing a processingcircuit that may be adapted according to certain aspects disclosedherein.

FIG. 18 is a flowchart illustrating a method for operating a wirelesscharging device in accordance with certain aspects disclosed herein.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of wireless charging systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawing by various blocks, modules, components,circuits, steps, processes, algorithms, etc. (collectively referred toas “elements”). These elements may be implemented using electronichardware, computer software, or any combination thereof. Whether suchelements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode,hardware description language, or otherwise. The software may reside ona processor-readable storage medium. A processor-readable storagemedium, which may also be referred to herein as a computer-readablemedium may include, by way of example, a magnetic storage device (e.g.,hard disk, floppy disk, magnetic strip), an optical disk (e.g., compactdisk (CD), digital versatile disk (DVD)), a smart card, a flash memorydevice (e.g., card, stick, key drive), Near Field Communications (NFC)token, random access memory (RAM), read only memory (ROM), programmableROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM),a register, a removable disk, a carrier wave, a transmission line, andany other suitable medium for storing or transmitting software. Thecomputer-readable medium may be resident in the processing system,external to the processing system, or distributed across multipleentities including the processing system. Computer-readable medium maybe embodied in a computer-program product. By way of example, acomputer-program product may include a computer-readable medium inpackaging materials. Those skilled in the art will recognize how best toimplement the described functionality presented throughout thisdisclosure depending on the particular application and the overalldesign constraints imposed on the overall system.

Overview

Certain aspects of the present disclosure relate to systems, apparatusand methods applicable to wireless charging devices and techniques.Charging cells may be configured with one or more inductive coils toprovide a charging device that can charge one or more deviceswirelessly. The location of a device to be charged may be detectedthrough sensing techniques that associate location of a device tochanges in a physical characteristic centered at a known location on asurface of the charging device. Sensing of location may be implementedusing capacitive, resistive, inductive, touch, pressure, load, strain,and/or another appropriate type of sensing.

In one aspect of the disclosure, an apparatus has a battery chargingpower source, a plurality of charging cells configured in a matrix, afirst plurality of switches in which each switch is configured to couplea row of power transmitting coils in the matrix to a first terminal ofthe battery charging power source, and a second plurality of switches inwhich each switch is configured to couple a column of power transmittingcoils in the matrix to a second terminal of the battery charging powersource. Each charging cell in the plurality of charging cells mayinclude one or more coils surrounding a power transfer area. Theplurality of power transmitting charging cells may be arranged adjacentto a charging surface without overlap of power transfer areas of thecharging cells in the plurality of charging cells. In some examples,each power transmitting coil may be directly driven by a driver circuit.

Certain aspects of the present disclosure relate to systems, apparatusand methods for wireless charging. In one example, each charging circuitin a plurality of charging circuits includes a power transmitting coiland a capacitor coupled at a node. One or more driver circuits areconfigurable to provide a charging current to one or more chargingcircuits in the plurality of charging circuits. A controller may beconfigured to cause a first pulse to be transmitted through each of theplurality of charging circuits, determine peak voltage at each of thenodes in the plurality of charging circuits, the peak voltage at eachnode being responsive to the first pulse and indicative of a couplingcoefficient with a receiving coil in a chargeable device, determine thata minimum peak voltage responsive to the first pulse is associated witha first charging circuit in the plurality of charging circuits, andconfigure the driver circuit to provide a first charging current to thefirst charging circuit.

Charging Cells

According to certain aspects disclosed herein, a charging device may beprovided using charging cells that are deployed adjacent to a surface ofthe charging device. In one example the charging cells are deployed inaccordance with a honeycomb packaging configuration. A charging cell maybe implemented using one or more coils that can each induce a magneticfield along an axis that is substantially orthogonal to the surface ofthe charging device and adjacent to the coil. In this description, acharging cell may refer to an element having one or more coils whereeach coil is configured to produce an electromagnetic field that isadditive with respect to the fields produced by other coils in thecharging cell, and directed along or proximate to a common axis.

In some implementations, a charging cell includes coils that are stackedalong a common axis and/or that overlap such that they contribute to aninduced magnetic field substantially orthogonal to the surface of thecharging device. In some implementations, a charging cell includes coilsthat are arranged within a defined portion of the surface of thecharging device and that contribute to an induced magnetic field withinthe substantially orthogonal portion of the surface of the chargingdevice associated with the charging cell. In some implementations,charging cells may be configurable by providing an activating current tocoils that are included in a dynamically-defined charging cell. Forexample, a charging device may include multiple stacks of coils deployedacross a surface of the charging device, and the charging device maydetect the location of a device to be charged and may select somecombination of stacks of coils to provide a charging cell adjacent tothe device to be charged. In some instances, a charging cell mayinclude, or be characterized as a single coil. However, it should beappreciated that a charging cell may include multiple stacked coilsand/or multiple adjacent coils or stacks of coils. The coils may bereferred to herein as charging coils, wireless charging coils,transmitter coils, transmitting coils, power transmitting coils, powertransmitter coils, or the like.

FIG. 1 illustrates an example of a charging cell 100 that may bedeployed and/or configured to provide a charging device. In thisexample, the charging cell 100 has a substantially hexagonal shape thatencloses one or more coils 102 constructed using conductors, wires orcircuit board traces that can receive a current sufficient to produce anelectromagnetic field in a power transfer area 104. In variousimplementations, some coils 102 may have a shape that is substantiallypolygonal, including the hexagonal charging cell 100 illustrated inFIG. 1. Other implementations may provide coils 102 that have othershapes. The shape of the coils 102 may be determined at least in part bythe capabilities or limitations of fabrication technology, and/or tooptimize layout of the charging cells on a substrate 106 such as aprinted circuit board substrate. Each coil 102 may be implemented usingwires, printed circuit board traces and/or other connectors in a spiralconfiguration. Each charging cell 100 may span two or more layersseparated by an insulator or substrate 106 such that coils 102 indifferent layers are centered around a common axis 108.

FIG. 2 illustrates the arrangement of power transfer areas providedacross a surface 200 of the charging device that employs multiple layersof charging cells configured in accordance with certain aspectsdisclosed herein. The charging device may be constructed from fourlayers of charging cells 202, 204, 206, 208. In FIG. 2, each powertransfer area provided by a charging cell in the first layer of chargingcells 202 is marked “L1”, each power transfer area provided by acharging cell in the second layer of charging cells 204 is marked “L2”,each power transfer area provided by a charging cell in the third layerof charging cells 206, 208 is marked “L3”, and each power transfer areaprovided by a charging cell in the first layer of charging cells 208 ismarked “L4”. FIG. 3 illustrates a wireless transmitter 300 that may beprovided in a charger base station. A controller 302 may receive afeedback signal filtered or otherwise processed by a filter circuit 308.The controller may control the operation of a driver circuit 304 thatprovides an AC signal to a resonant circuit 306 that includes acapacitor 312 and inductor 314. The resonant circuit 306 may also bereferred to herein as a tank circuit, an LC tank circuit and/or as an LCtank, and the voltage 316 measured at an LC node 310 of the resonantcircuit 306 may be referred to as the tank voltage.

The wireless transmitter 300 may be used by a charging device todetermine if a compatible device has been placed on a surface of thecharging device. For example, the charging device may determine that acompatible device has been placed on the surface of the charging deviceby sending an intermittent test signal (active ping) through thewireless transmitter 300, where the resonant circuit 306 may receiveencoded signals when a compatible device responds to the test signal.The charging device may be configured to activate one or more coils inat least one charging cell after receiving a response signal defined bystandard, convention, manufacturer or application. In some examples, thecompatible device can respond to a ping by communicating received signalstrength such that the charging device can find an optimal charging cellto be used for charging the compatible device.

In accordance with certain aspects disclosed herein, a charging devicemay use one or more location sensing techniques to detect placement ormovement of objects on a surface of the charging device. In certainexamples, location sensing techniques rely on changes in some propertyof the electrical conductors that form coils in a charging cell.Measurable differences in properties of the electrical conductors mayinclude capacitance, resistance, inductance and/or temperature. In someexamples, loading of a surface of the charging device can affect themeasurable resistance of a coil located near the point of loading. Insome implementations, sensors may be provided to enable location sensingthrough detection of changes in touch, pressure, load and/or strain.

A controller in the charging device may attempt to determine the natureof the object. When the controller determines that the object is achargeable, the controller may attempt to identify the chargeable deviceand the capabilities of the chargeable device. The controller maydetermine a charging configuration that may be used to charge thechargeable device, including one or more coils to receive correspondingcharging currents, and the magnitude, frequency and phase of eachcharging current. In one example, the controller may initiate a digitalping procedure to identify a charging cell, a combination of chargingcells and/or a combination of coils that are to be activated to chargethe device placed on the charging surface. The digital ping procedureverifies that the device to be charged is compatible with the chargingdevice, and may identify a signal strength indicating whether the coilsused to transmit the digital ping are best positioned for the requestedor desired charging procedure.

Significant power savings can be achieved when a search is conducted tolocate a device placed on or near in a multi-coil, free positioncharging pad before using digital pings to establish that the device isconfigured to receive charge from a wireless charging device. Thesavings in power consumption can be obtained by refraining fromproviding digital pings until a device is detected in a search, and bylimiting digital ping transmissions to transmitting coils that areplaced in proximity to the detected device and likely to be capable ofestablishing an electromagnetic charging connection with the detecteddevice.

Wireless charging devices may be adapted in accordance with certainaspects disclosed herein to support a low-power discovery technique thatcan replace and/or supplement conventional ping transmissions. Aconventional ping is produced by driving a resonant LC circuit thatincludes a transmitting coil of a base station. The base station thenwaits for an ASK-modulated response from the receiving device. Alow-power discovery technique may include utilizing a passive ping toprovide fast and/or low-power discovery. According to certain aspects, apassive ping may be produced by driving a network that includes theresonant LC circuit with a pulse that includes a small amount of energy.The pulse may be provided using an alternating current (AC) voltage orcurrent. In some implementations, the pulse has a duration that is lessthan the period of the voltage or current used to excite the resonant LCcircuit. In one example, the fast pulse may have a durationcorresponding to a half cycle of the resonant frequency of the networkand/or the resonant LC circuit. In some implementations, the pulseincludes multiple cycles of the voltage or current used to excite theresonant LC circuit. The pulse causes the network to oscillate at itsnatural resonant frequency until the injected energy decays and isdissipated. When the base station is configured for wirelesstransmission of power within the frequency range 100 kHz to 200 kHz, thefast pulse may have a duration that is less than 2.5 μs.

The passive ping may be characterized and/or configured based on thenatural frequency at which the network including the resonant LC circuitrings, and the rate of decay of energy in the network. The ringingfrequency of the network and/or resonant LC circuit may be defined as:

$\begin{matrix}{\omega = \frac{1}{\sqrt{LC}}} & ( {{Eq}.\mspace{14mu} 1} )\end{matrix}$

The rate of decay is controlled by the quality factor (Q factor) of theoscillator network, as defined by:

$\begin{matrix}{Q = {\frac{1}{R}\sqrt{\frac{L}{C}}}} & ( {{Eq}.\mspace{14mu} 2} )\end{matrix}$

Equations 1 and 2 show that resonant frequency is affected by L and C,while the Q factor is affected by L, C and R. In a base station providedin accordance with certain aspects disclosed herein, the wireless driverhas a fixed value of C determined by the selection of the resonantcapacitor. The values of L and R are determined by the wirelesstransmitting coil and by an object or device placed adjacent to thewireless transmitting coil.

The wireless transmitting coil is configured to be magnetically coupledwith a receiving coil in a device placed within close proximity of thetransmitting coil, and to couple some of its energy into the proximatedevice to be charged. The L and R values of the transmitter circuit canbe affected by the characteristics of the device to be charged, and/orother objects within close proximity of the transmitting coil. As anexample, if a piece of ferrous material with a high magneticpermeability placed near the transmitter coils can increase the totalinductance (L) of the transmitter coil, resulting in a lower resonantfrequency, as shown by Equation 1. Some energy may be lost throughheating of materials due to eddy current induction, and these losses maybe characterized as an increase the value of R thereby lowering the Qfactor, as shown by Equation 2.

A wireless receiver placed in close proximity to the transmitter coilcan also affect the Q factor and resonant frequency. The receiver mayinclude a tuned LC network with a high Q which can result in thetransmitter coil having a lower Q factor. The resonant frequency of thetransmitter coil may be reduced due to the addition of the magneticmaterial in the receiver, which is now part of the total magneticsystem. Table 1 illustrates certain effects attributable to differenttypes of objects placed within close proximity to the transmitter coil.

TABLE 1 Object L R Q Frequency None present Base Value Base value BaseValue (High) Base Value Ferrous Small Increase Large Increase LargeDecrease Small Decrease Non-ferrous Small Decrease Large Increase LargeDecrease Small Increase Wireless Receiver Large Increase Small DecreaseSmall Decrease Large Decrease

In the example illustrated in FIG. 3, passive ping techniques may usethe voltage and/or current measured or observed at the LC node 310 toidentify the presence of a receiving coil in proximity to the chargingpad of a device adapted in accordance with certain aspects disclosedherein. In many conventional wireless charger transmitters, circuits areprovided to measure voltage at the LC node 310 or the current in thenetwork. These voltages and currents may be monitored for powerregulation purposes and/or to support communication between devices. Aresponse of the resonant circuit 306 to a passive ping (initial voltageV_(o)) may be represented by the voltage (V_(LC)) at the LC node 310such that:

$\begin{matrix}{V_{LC} = {V_{0}e^{{- {(\frac{\omega}{2Q})}}t}}} & ( {{Eq}.\mspace{14mu} 3} )\end{matrix}$

According to certain aspects disclosed herein, coils in one or morecharging cells may be selectively activated to provide an optimalelectromagnetic field for charging a compatible device. In someinstances, coils may be assigned to charging cells, and some chargingcells may overlap other charging cells. In the latter instances, theoptimal charging configuration may be selected at the charging celllevel. In other instances, charging cells may be defined based onplacement of a device to be charged on a surface of the charging device.In these other instances, the combination of coils activated for eachcharging event can vary. In some implementations, a charging device mayinclude a driver circuit that can select one or more cells and/or one ormore predefined charging cells for activation during a charging event.

FIG. 4 illustrates a first example in which a response 400 to a passiveping decays according to Equation 3. After the excitation pulse at timet=0, the voltage and/or current is seen to oscillate at the resonantfrequency defined by Equation 1, and with a decay rate defined byEquation 3. The first cycle of oscillation begins at voltage level Voand VIE continues to decay to zero as controlled by the Q factor and ω.The example illustrated in FIG. 4 represents a typical open or unloadedresponse when no object is present or proximate to the charging pad. InFIG. 4 the value of the Q factor is assumed to be 20.

FIG. 5 illustrates a second example in which a response 500 to a passiveping decays according to Equation 3. After the excitation pulse attime=0, the voltage and/or current is seen to oscillate at the resonantfrequency defined by Equation 1, and with a decay rate defined byEquation 3. The first cycle of oscillation begins at voltage level V_(o)and V_(LC) continues to decay to zero as controlled by the Q factor andω. The example illustrated in FIG. 5 represents a loaded response whenan object is present or proximate to the charging pad loads the coil. InFIG. 4 the Q factor may have a value of 7. V_(LC) oscillates at a higherin the response 500 with respect to the response 400.

FIG. 6 illustrates a set of examples in which differences in responses600, 620, 640 may be observed. A passive ping is initiated when a drivercircuit 304 excites the resonant circuit 306 using a pulse that isshorter than 2.5 μs. Different types of wireless receivers and foreignobjects placed on the transmitter result in different responsesobservable in the voltage at the LC node 310 or current in the resonantcircuit 306 of the transmitter. The differences may indicate variationsin the Q factor of the resonant circuit 306 frequency of the oscillationof V_(o). Table 2 illustrates certain examples of objects placed on thecharging pad in relation to an open state.

TABLE 2 50% V_(peak) Decay Q Object Frequency (mV) Cycles Factor Nonepresent  96.98 kHz 134 mV 4.5 20.385 Type-1 Receiver  64.39 kHz  82 mV3.5 15.855 Type-2 Receiver  78.14 kHz  78 mV 3.5 15.855 Type-3 Receiver 76.38 kHz 122 mV 3.2 14.496 Misaligned Type-3 Receiver 210.40 kHz 110mV 2.0  9.060 Ferrous object  93.80 kHz 110 mV 2.0  9.060 Non-ferrousobject 100.30 kHz 102 mV 1.5  6.795In Table 2, the Q factor may be calculated as follows:

$\begin{matrix}{{Q = {\frac{\pi N}{\ln \; (2)} \cong {{4.5}3N}}},} & ( {{Eq}.\mspace{14mu} 4} )\end{matrix}$

where N is the number of cycles from excitation until amplitude fallsbelow 0.5 V_(o).

FIG. 7 is a flowchart 700 that illustrates a method involving passiveping implemented in a wireless charging device adapted in accordancewith certain aspects disclosed herein. At block 702, a controller maygenerate a short excitation pulse and may provide the short excitationpulse to a network that includes a resonant circuit. The network mayhave a nominal resonant frequency and the short excitation pulse mayhave a duration that is less than half the nominal resonant frequency ofthe network. The nominal resonant frequency may be observed when thetransmitting coil of the resonant circuit is isolated from externalobjects, including ferrous objects, non-ferrous objects and/or receivingcoils in a device to be charged.

At block 704, the controller may determine the resonant frequency of thenetwork or may monitor the decay of resonation of the network responsiveto the pulse. According to certain aspects disclosed herein, theresonant frequency and/or the Q factor associated with the network maybe altered when a device or other object is placed in proximity to thetransmitting coil. The resonant frequency may be increased or decreasedfrom the nominal resonant frequency observed when the transmitting coilof the resonant circuit is isolated from external objects. The Q factorof the network may be increased or decreased with respect to a nominal Qfactor measurable when the transmitting coil of the resonant circuit isisolated from external objects. According to certain aspects disclosedherein, the duration of delay can be indicative of the presence or typeof an object placed in proximity to the transmitting coil whendifferences in Q factor prolong or accelerate decay of amplitude ofoscillation in the resonant circuit with respect to delays associatedwith a nominal Q factor.

In one example, the controller may determine the resonant frequency ofthe network using a transition detector circuit configured to detectzero crossings of a signal representative of the voltage at the LC node310 using a comparator or the like. In some instances, direct current(DC) components may be filtered from the signal to provide a zerocrossing. In some instances, the comparator may account for a DCcomponent using an offset to detect crossings of a common voltage level.A counter may be employed to count the detected zero crossings. Inanother example the controller may determine the resonant frequency ofthe network using a transition detector circuit configured to detectcrossings through a threshold voltage by a signal representative of thevoltage at the LC node 310, where the amplitude of the signal is clampedor limited within a range of voltages that can be detected and monitoredby logic circuits. In this example, a counter may be employed to counttransitions in the signal. The resonant frequency of the network may bemeasured, estimated and/or calculated using other methodologies.

In another example, a timer or counter may be employed to determine thetime elapsed for V_(LC) to decay from voltage level V_(o) to a thresholdvoltage level. The elapsed time may be used to represent a decaycharacteristic of the network. The threshold voltage level may beselected to provide sufficient granularity to enable a counter or timerto distinguish between various responses 600, 620, 640 to the pulse.V_(LC) may be represented by detected or measured peak, peak-to-peak,envelope 602 and/or rectified voltage level. The decay characteristic ofthe network may be measured, estimated and/or calculated using othermethodologies.

If at block 706, the controller determines that a change in resonantfrequency with respect to a nominal resonant frequency indicate presenceof an object in proximity to the transmitting coil, the controller mayattempt to identify the object at block 712. If the controllerdetermines at block 706 that resonant frequency is substantially thesame as the nominal resonant frequency, the controller may consider thedecay characteristic of the amplitude of oscillation in the resonantcircuit at block 708. The controller may determine that the resonantfrequency of the network is substantially the same as the nominalresonant frequency when the frequency remains within a defined frequencyrange centered on, or including the nominal resonant frequency. In someimplementations, the controller may identify objects using changes inresonant frequency and decay characteristics. In these latterimplementations, the controller may continue at block 708 regardless ofresonant frequency, and may use changes in change in resonant frequencyas an additional parameter when identifying an object positionedproximately the transmission coil.

At block 708, the controller may use a timer and/or may count the cyclesof the oscillation in the resonant circuit that have elapsed between theinitial V_(O) amplitude and a threshold amplitude used to assess thedecay characteristic. In one example, V_(O)/2 may be selected as thethreshold amplitude. At block 710, the number of cycles or the elapsedtime between the initial V_(O) amplitude and the threshold amplitude maybe used to characterize decay in the amplitude of oscillation in theresonant circuit, and to compare the characterize decay with acorresponding nominal decay characteristic. If at block 710, no changein frequency and delay characteristic is detected, the controller mayterminate the procedure with a determination that no object isproximately located to the transmission coil. If at block 710, a changein frequency and/or delay characteristic has been detected, thecontroller may identify the object at block 712.

At block 712, the controller may be configured to identify receivingdevices placed on a charging pad. The controller may be configured toignore other types of objects, or receiving devices that are notoptimally placed on the charging pad including, for example, receivingdevices that are misaligned with the transmission coil that provides thepassive ping. In some implementations, the controller may use a lookuptable indexed by resonant frequency, decay time, change in resonantfrequency, change in decay time and/or Q factor estimates. The lookuptable may provide information identifying specific device types, and/orcharging parameters to be used when charging the identified device ortype of device.

Passive ping uses a very short excitation pulse that can be less than ahalf-cycle of the nominal resonant frequency observed at the LC node 310in the resonant circuit 306. A conventional ping may actively drive atransmission coil for more than 16,000 cycles. The power and timeconsumed by a conventional ping can exceed the power and time use of apassive ping by several orders of magnitude. In one example, a passiveping consumes approximately 0.25 μJ per ping with a max ping time ofaround ˜100 μs, while a conventional active ping consumes approximately80 mJ per ping with a max ping time of around 90 ms. In this example,energy dissipation may be reduced by a factor of 320,000 and the timeper ping may be reduced by a factor of 300.

Detection and characterization of the decay of the voltage at the LCnode 310 may require fast, sensitive and/or low-voltage circuits toaccommodate the low-power nature of resonant signals at the LC node 310when a short excitation pulse is used to produce resonant signals in theresonant circuit 306. In some instances, passive ping may be implementedusing a burst of energy at the nominal resonant frequency of theresonant circuit 306. The burst of energy may have a duration of severalperiods of the nominal resonant frequency. This burst-mode passive pingnecessarily consumes more energy per ping that passive ping that isinitiated by short excitation pulses. The additional energy providesadditional time to characterize resonant response.

FIG. 8 illustrates a first example of the frequency responses 800 of theresonant circuit 306 when the resonant circuit 306 is stimulated by aping that includes several cycles of a signal that oscillates at or nearthe nominal resonant frequency (f_(o) 802) of the resonant circuit 306.A first frequency response 804 illustrates the response of the resonantcircuit 306 when no device is present, while a second frequency response806 illustrates the response of the resonant circuit 306 when achargeable object is present. The chargeable object reduces the Q-factorof the resonant circuit 306. The higher Q-factor of the resonant circuit306 when no device is present causes the resonant circuit 306 to producea significantly higher voltage response 808 and draw the maximum currentwith the longest decay time in response to a passive ping at f_(o) 802than the voltage response 810 produced when a chargeable device lowersthe Q-factor of the resonant circuit 306, causing the resonant circuit306 to produce lower voltage, draw less current and have a shorter decaytime in response to a passive ping at f_(o) 802. In typicalapplications, no object is present for a majority of the time a chargingdevice is in operation, and the resonant circuit 306 in the chargingdevice has a high Q-factor for a majority of the time. The high Q-factorresults in a high power draw. The resonant circuit 306 has a slowerresponse time when it has a high Q-factor, since more time is needed forthe ping energy to decay thereby delaying initiation of another ping.

FIG. 9 illustrates a second example of frequency responses 900 of theresonant circuit 306 illustrating the effect of a ping provided as amulti-period burst at a frequency (f_(p) 902) that is greater than thenominal resonant frequency (f_(o) 908) of the resonant circuit 306. Insome implementations, the ping is provided as a multi-period burst at afrequency that is lower than f_(o) 908. In this example, the dominantstate of the charging device, where no chargeable object is present,results in a lower power draw and faster decay rate resulting in fasterperformance with respect to the example illustrated in FIG. 8. The pingprocess results in limited higher-power draw and increased decay ratethat occurs for the ping that leads to detection of a chargeable object.Additional passive pings are typically superfluous after detection.

The resonant circuit 306 may be stimulated during passive ping by asignal that has a duration that can include several cycles at f_(p) 902.A first frequency response 904 illustrates the response of the resonantcircuit 306 when no device is present, while a second frequency response906 illustrates the response of the resonant circuit 306 when achargeable object is present. The chargeable object reduces the Q-factorof the resonant circuit 306. The resonant circuit 306 produces asignificantly lower voltage response 910 and draws a lower current witha shorter decay time in response to a passive ping at f_(p) 902 when nodevice is present than the voltage response 912 produced when achargeable device is present. In typical applications, no object ispresent for a majority of the time a charging device is in operation,and the resonant circuit 306 exhibits a lower power consumption and afaster decay time per ping with respect to the example illustrated inFIG. 8.

The frequency spread (f_(p)-f_(o) or f_(o)-f_(p)) between the resonantfrequency (f_(o) 908) and the ping frequency (f_(p) 902) may beproportionate to the value of f_(o) 908. For example, the frequencyspread may increase as f_(o) 908 increases. In some implementations, thefrequency spread and f_(o) 908 a have a logarithmic (log base 10)relationship. In an example that is compliant or compatible with Qistandards, where 80 Khz<f_(o)<110 Khz, a passive ping frequency may bedefined such that 175 KHz<f_(p)<210 KHz.

According to certain aspects disclosed herein, frequency spread may beselected as a trade-off between signal-to-noise ratio (SNR) and powerconsumption or response time. In the example illustrated in FIG. 9, anoverly-high value for frequency spread may result in lower SNR, while anoverly-high value for frequency spread may result in high power drawand/or slow response. The optimal balance between SNR and power draw mayvary by application. In some implementations, the lowest power and fastscan rate is obtained by setting f_(p) 902 as high as possible whilepermitting reliable detection of objects given SNR for the system.

The duration of a passive ping pulse can be defined as a number offraction of cycles of f_(p) 902. In one example, the duration of thepassive ping pulse may be set to a half-cycle of f_(p) 902. In anotherexample, the duration of the passive ping pulse may be set to multiplecycles of f_(p) 902. In some implementations, the duration of thepassive ping pulse includes enough half-cycles of f_(p) 902 to obtain acurrent draw in the detectable range of an analog-to-digital converter(ADC) in microprocessor of a charging device. The passive ping pulse mayinclude additional cycles to accommodate the SNR margin. The number ofadditional cycles may be the subject of a trade-off to increase the SNR,while limiting power and ping time. In one example, where f_(p)=190 KHzand f_(o)=100 KHz, the duration of the passive ping pulse is less than1000 μS.

The repetition rate for passive ping pulses can be determineddynamically when speed of detection is prioritized. In one example, theADC can be checked to determine when current has fallen back to zerobefore starting the next passive ping pulse. In this manner, a detectioncircuit can determine that no energy remains in the resonant circuit 306from the previous ping pulse before initiating the next passive pingpulse. In some implementations, a fixed delay between pulses may beimplemented. In one example, the fixed delay may be configured to be 6tomes the longest decay time constant expected or observed in theresonant circuit 306. In one example, the fixed delay may be configuredto provide a one millisecond interval between pulses. The onemillisecond ping interval may enable an 18 coil charging pad to bescanned in 18 mS, permitting sub-second device detection. The fixed timeapproach can be used if further optimization for speed is not necessary.When larger numbers of charging coils are provided in a charging pad, adynamic ping interval may be used.

According to certain aspects disclosed herein, coils in one or morecharging cells may be selectively activated to provide an optimalelectromagnetic field for charging a compatible device. In someinstances, coils may be assigned to charging cells, and some chargingcells may overlap other charging cells. In the latter instances, theoptimal charging configuration may be selected at the charging celllevel. In other instances, charging cells may be defined based onplacement of a device to be charged on a charging surface. In theseother instances, the combination of coils activated for each chargingevent can vary. In some implementations, a charging device may include adriver circuit that can select one or more cells and/or one or morepredefined charging cells for activation during a charging event.

Dynamic Inferred Coupling Estimation

Certain aspects of this disclosure relate to detection of an optimal oroptimized charging configuration in a wireless charging system,including charging systems adapted for concurrent charging of multipledevices or batteries. Optimization of a charging configuration may beconducted when a device or battery to be charged can be placed on ornear different transmitter coils on a surface provided by the chargingdevice. The charging configuration may be determined by detecting one ormore charging coils that exhibit best coupling to the receiving deviceor battery.

FIG. 10 illustrates an example 1000 of coupling in a wireless chargingsystem 1002 that includes multiple charging coils 1004 ₁-1004 _(n). Thewireless charging system 1002 may be configured to charge a device orbattery (receiving device 1006) based on placement near one of a numberof different sections of the charging area provided by the chargingcoils 1004 ₁-1004 _(n). In the illustrated example 1000, the receivingdevice 1006 is closely aligned with a first charging coil 1004 ₁ andproximate to one or more other charging coils 1004 ₂-1004 _(n). Thereceiving device 1006 is well-coupled to the first charging coil 1004 ₁,with a relatively strong flux 1010 coupling the receiving device 1006 tothe first charging coil 1004 ₁ when the first charging coil 1004 ₁ isactivated. The receiving device 1006 may be poorly-coupled to othercharging coils 1004 ₂-1004 _(n), and few lines of flux 1012, 1014 couplethe receiving device 1006 to the other charging coils 1004 ₂-1004 _(n)when the first charging coil 1004 ₁ is activated. The coupling betweenthe receiving device 1006 and the other charging coils 1004 ₂-1004 _(n)may be referred to as parasitic coupling.

The higher quality coupling between the receiving device 1006 and thefirst charging coil 1004 ₁ can result in superior power transferefficiency. The higher quality coupling reduces the reactive powerrequired by the primary LC of the first charging coil 1004 ₁. Loweredreactive power results in lower losses due to lower power dissipation inparasitic resistances in the first charging coil 1004 ₁.

The higher quality coupling between the receiving device 1006 and thefirst charging coil 1004 ₁ can produce uncontained magnetic flux (seethe lines of flux 1012, 1014 coupling the receiving device 1006 to theother charging coils 1004 ₂-1004 _(n)). Uncontained magnetic flux maycouple the first charging coil 10041 with other devices and/or objects,resulting in interference as well as losses resulting from eddy currentsinduced in metal objects. Uncontained flux can also result in a largerelectromagnetic interference (EMI) signature, and can increase radiointerference. Increased radio interference may prevent the wirelesscharging system 1002 to from complying with regulatory standards for EMIpromulgated by government entities such as standards defined by theUnited States Federal Communications Commission (FCC) and the standardsassociated with the CE mark of the European Economic Area.

When multiple Tx coils and receiving coils are near, or are parts of thesame system, crosstalk can result. For example, crosstalk can resultwhen multiple charging coils 1004 ₁-1004 _(n) are located within awireless charging system 1002 used to charge the receiving device 1006.Crosstalk can cause digital messages exchanged between transmitter andreceiver where digital messages between a pair of devices may bereceivable by a third device. FIG. 11 illustrates a charging environment1100 in which a receiving device 1102 and a charging device 1104exchange messages including digital pings 1106 and received powerreports 1108. Crosstalk can disrupt messaging between the receivingdevice 1102 and the charging device 1104, resulting in unreliableoperation of a wireless charging system 1002.

Certain aspects of the disclosure enable a coupling configuration to bedetermined in real-time, enabling a power transmitter to distinguishbetween power signals from well-coupled devices and from more distant,more poorly-coupled devices. The availability of coupling configurationinformation enables a pair of well-coupled devices to filter or ignoretransmissions from poorly-coupled devices or charging coils, therebypreventing or reducing erroneous charging operations.

As disclosed herein, certain methods for detecting coupling in wirelesscharging systems include the two-step process illustrated in FIG. 11.The charging device 1104 transmits a digital ping 1106 when it detects apotentially chargeable device. The receiving device 1102 responds bytransmitting a protocol-defined response to the digital ping 1106. Inthe illustrated example, the response includes a power report 1108 thatmay inform the charging device 1104 of the received power level asdetermined by the receiving device 1102. Certain aspects disclosedherein address the disadvantages observed in conventional systems thatinclude slow detection and negotiation and the quantity of energyrequired to be sent in the digital ping 1106 to enable measurement ofreceived power. When multiple charging coils 1004 ₁-1004 _(n) and areoperated concurrently in a wireless charging system 1002, then two ormore charging coils 1004 ₁-1004 _(n) may send a digital ping 1106 whensearching or confirming presence of potentially chargeable devices,resulting in increased time and power consumption. Parasitic messagesfrom nearby, poorly-coupled devices may inhibit or prohibit a powertransmitter from querying potentially chargeable devices. In someinstances, the charging device may mistakenly respond to the parasiticmessages.

Certain aspects of this disclosure provide for Dynamic Inferred CouplingEstimation (DICE) in order to detect quality of coupling in real-time.In one example, DICE includes an evaluation of the ratio of real powerto reactive power in a circuit that includes a transmitting coil andseries resonant capacitor. The amount of reactive power stored in theinductor-capacitor (LC) circuit of the transmitter is substantiallyinfluenced by the coupling coefficient. The coupling coefficient definesthe ratio of mutual inductance to leakage inductance in the LC circuitof the wireless transmitter. For example, leakage inductance in the LCcircuit of the wireless transmitter may be expressed as:

TX _(leakage) =L _(TX)×(1−k),   (Eq. 5)

where L_(Tx) represents the self-inductance of the transmitter coil, andk represents the coupling coefficient. Decreasing coupling reducescoupling coefficient and increases leakage inductance, resulting in morereactive energy being stored in the leakage inductance of thetransmitter. Energy stored in the leakage inductance does not contributeto power transfer and, as energy builds up in the leakage inductance,the voltage at the LC node increases.

Certain aspects of the coupling between one or more charging coils 1004₁-1004 _(n) and a receiving device 1006 may be characterized by voltagemeasured at the LC node. Voltage measurements taken at the LC node maybe available for other reasons. In some instances, voltage at the LCnode may be monitored as an overvoltage indicator used to protect powerelectronics and the resonant capacitor. In one example, the measurementcircuit includes a voltage comparator configured to detect voltagesexceeding a threshold level. According to certain aspects disclosedherein, a measurement circuit may be added, or an existing measurementcircuit may be used to quantify or compare a voltage at the LC node thatvaries directly with the quality of coupling.

Referring again to Eq. 5, when k is close in value to 1, the voltage ofthe LC node may be near that of the driving source voltage, as therewould be substantially no stored energy attributable to the leakageinductance, and no voltage increase due to stored energy in the leakageinductance. As coupling decreases, leakage inductance increases, andenergy is stored in the LC circuit of the transmitter. This storedenergy may be accompanied by an increase in voltage and/or current inthe LC circuit of the transmitter. The resultant additional reactiveenergy may have the secondary effect of dissipating additional power inthe parasitic resistance associated with the LC circuit of thetransmitter. These extra losses can cause a high input power draw forthe same output power delivered to the load in the receiver, and aresultant reduction in overall system efficiency.

The tables 1200, 1220, 1240 in FIG. 12 illustrate the effect of couplingon voltage measured at the LC circuit of the transmitter in a wirelesscharging system 1002. Each table 1200, 1220, 1240 lists measurementsthat correspond to a power transfer from a transmitter to a receiverthat is connected to fixed load, where the coupling of the system isadjusted by incrementing the separation between the transmitter andreceiver using spacers, which may be formed as plastic shims. In thefirst table 1200, the receiver is connected to a 100 mA load, in thesecond table 1220, the receiver is connected to no load (0 mA), and inthe third table 1240, the receiver is connected to a 250 mA load. Thetables 1200, 1220, 1240 illustrate that input current (Lin) varies withload and spacing, while the peak voltage (Vpk) measured at the LC nodevaries substantially with changes in coupling and is substantiallyindependent of changes in load.

According to certain aspects of the disclosure, Vpk measured at the LCnode may be used as a stable metric for detecting changes in couplingcoefficient. With reference to FIG. 13, the metric may be used todetermine the optimal charging configuration when a chargeable device1308 has been placed on a charging surface 1300, 1320 of a multi-driver,free-position charger, and/or to detect real-time changes 1332 inreceiver position.

In one aspect, the use of a metric to characterize coupling coefficientin real-time allows the charging system to determine the optimalcharging configuration. The optimal charging configuration may identifythe best charging coil 1302, 1304, 1306 to be used for power transfer toa chargeable device 1308. The optimal charging configuration may providean optimal power level that permits the chargeable device 1308 to becharged at an optimal rate while minimizing losses due to parasiticeffects. The best coil 1304 for charging may be selected from multiplecharging coils 1302, 1304, 1306 based on a comparison of metrics derivedfrom Vpk measurements.

In some implementations, a modified active ping process may beimplemented to select an optimal charging configuration. Conventionally,a transmitter in a wireless power transmitting system fully powers eachcharging coil 1302, 1304, 1306 in turn. The transmitter waits fordigital communications to be established in order to check theconnection quality. The transmitter repeats the process for each ofcharging coil 1302, 1304, 1306.

A wireless power transmitting system adapted in accordance with certainaspects disclosed herein may employ DICE to select an optimal chargingconfiguration. A small packet of energy may be sent to each candidatecharging coil 1302, 1304, 1306. In some implementations, the smallpacket of energy may be sent to all candidate charging coils 1302, 1304,1306 at the same time. In one example, the charging coil 1304 with thelowest Vpk may be selected for power transfer, where the lowest Vpk isindicative of highest coupling.

In one aspect, the use of a metric to characterize coupling in real-timecan allow the charging system to detect real-time changes in receiverposition. A free-position charging system is typically required torespond to movement of a chargeable device 1330 from an originalposition 1328 across a charging surface during charging. Conventionalwireless charging systems generally cannot gracefully react to suddenchanges in position of a chargeable device 1330. In these conventionalsystems, the charging must be stopped the charging system mustrenegotiate with the chargeable device 1330 through a new charging coil1326 after the charging device has detected the relocated chargeabledevice 1330.

A wireless power transmitting system adapted in accordance with certainaspects disclosed herein may employ DICE to detect movement of areceiving chargeable device 1330, including when the chargeable device1330 is moving or has moved before without fully disconnected from itscurrent charging coil charging coils 1322 or 1324. In one example, thecharging device can determine that Vpk has exceeded a pre-set thresholdvalue, and may activate one or more adjacent charging coils 1302, 1304,1306 to commence immediate evaluation of coupling. As soon as couplingin an adjacent charging coil 1302, 1304, 1306 becomes better thancoupling in the active charging coil 1302 or 1304, power transfer can betransitioned to the new charging coil 1306. The chargeable device 1330may remain unaware that power transfer has transitioned between chargingcoils 1302, 1304, 1306, and the flow of power to the receiving devicemay be uninterrupted.

A wireless power transmitting system adapted in accordance with certainaspects disclosed herein may employ DICE to detect phantom receivers. Aphantom receiver may arise due to a type of erroneous operation thatoccurs when one of two or more devices being charged is removed from thecharging surface. The charging circuits associated with the removeddevice may see messages transmitted by remaining devices. The chargingcircuits associated with the removed device may continue charging whenthe removal of the device is not detected because of messages receivedfrom one or more remaining devices. According to certain aspectsdisclosed herein, the wireless power transmitting system may check LCnode voltage in the charging circuits associated with the removed deviceand may thereby detect an abnormally high Vpk while input current drawis low. The wireless power transmitting system may deduce that themessages are not received from a well-coupled power receiver. In someinstances, phantom devices may be detected using DICE and a “sneak-away”algorithm.

Sneak-Away

FIGS. 14 and 15 illustrate an example of removal of a charging devicethat may result in a wireless power transmitting system detecting aphantom receiver. In a first configuration 1400, a wireless chargingsystem 1402 includes multiple charging coils 1404 ₁-1404 _(n) that canconcurrently charge multiple devices or batteries (receiving devices1406, 1408), which may be placed near different sections of the chargingarea provided by the charging coils 1404 ₁-1404 _(n). In the illustratedexample 1400, a first receiving device 1406 is closely aligned with afirst charging coil 1404 ₁ and proximate to one or more other chargingcoils 1404 ₂-1404 _(n), while a second receiving device 1408 is closelyaligned with an n^(th) charging coil 1404 _(n) and proximate to one ormore other charging coils 1404 ₁, 1404 ₂. The first receiving device1406 is well-coupled to the first charging coil 1404 ₁, and the secondreceiving device 1408 is well-coupled to the n^(th) charging coil 1404_(n). The receiving devices 1406, 1408 may be poorly-coupled to othercharging coils 1404 ₂-1404 _(n). and 1404 ₁-1404 _(n-1), respectively.

In a second configuration 1500, a wireless charging system 1502 includesmultiple charging coils 1504 ₁-1504 _(n) that can concurrently chargemultiple devices or batteries (receiving devices 1506, 1508), which canbe placed near different sections of the charging area provided by thecharging coils 1504 ₁-1504 _(n). In this example 1500, a first receivingdevice 1506 is closely aligned with a first charging coil 1504 ₁ andproximate to one or more other charging coils 1504 ₂-1504 _(n), while asecond receiving device 1508 had been closely aligned with an n^(th)charging coil 1504 _(n) but has now been removed from the vicinity ofthe wireless charging system 1502. The first receiving device 1506 iswell-coupled to the first charging coil 1504 ₁, and may bepoorly-coupled to other charging coils 1504 ₂-1504 _(n).

Typically, when a receiving device 1506, 1508 is well-coupled with acharging coil 1504 ₁-1504 _(n), its communication signal is strongenough to overcome any parasitic flux from nearby drivers. In oneexample, an ASK detector used for communication operates at the high endof its dynamic range. When a receiving device 1508 is removed whileanother receiving device 1506 is still charging, the parasitic flux fromthe active receiving device 1506 subverts the flux from the removedreceiving device 1508. As the total field intensity on the now uncoupledcharging coil 1504 ₁ drops dramatically, the sensitivity of the ASKdetector shifts to the lower end of its dynamic range in an attempt todetect weak messages in the absence of a strong magnetic field. At thisnew high sensitivity, the uncoupled charging coil 1504 ₁ may detectmessages 1510 from the parasitic flux coupled from adjacent pads. Thecommunication channel associated with the active receiving device 1506starts to feed the uncoupled charging coil 1504 ₁ with messages 1510.This results in a phantom receiver detection that keeps the uncoupledcharging coil 1504 ₁ operating as if coupled to the removed receivingdevice 1508.

In one aspect of the disclosure, phantom receiver detection can beaverted using an algorithm (the Sneak-Away algorithm) that causes thewireless charging system 1502 to periodically test the power channel toensure that received messages derive from a well-coupled device ratherthan from an adjacent device.

In some implementations, the wireless charging system 1502 may reduceits power output through one of the active charging coils 1504 ₁-1504_(n). A receiving device 1506, 1508 coupled to the active charging coils1504 ₁-1504 _(n) is expected to respond to a reduction in power bysending a message instructing the wireless charging system 1502 toincrease its power output through the active charging coils 1504 ₁-1504_(n). If the receiving device 1506, 1508 does not respond with a requestto increase power, the wireless charging system 1502 may determine thatthe receiving device 1506, 1508 is not actively coupled to the chargingcoils 1504 ₁-1504 _(n) for which power was reduced, and the wirelesscharging system 1502 may conclude that messages related to the receivingdevice 1506, 1508 are received through parasitic coupling. The wirelesscharging system 1502 may cause any charging coils 1504 ₁-1504 _(n)associated with such phantom receivers to exit the active power transferstate and return to the selection state, allowing these charging coils1504 ₁-1504 _(n) to look for new chargeable devices.

In some implementations, multiple reductions in power are performed overa time period to improve phantom receiver detection. The reduction inpower applied may be small enough to avoid adversely affect thereceiver's load regulation performance, while being large enough toprompt the receiver to respond with a request to increase power.

FIG. 16 is a flowchart 1600 illustrating phantom receiver detection inaccordance with certain aspects disclosed herein. At block 1602, awireless charging system 1502 may initialize a coil counter that is usedto index or identify a charging coil 1504 ₁-1504 _(n) to participate ina search for phantom receivers. The coil counter may count continuouslysuch that, for example, the coil counter initially has a value of 1,counts to N and then resets to 1. In this manner a continuous check forphantom receivers may be conducted. At block 1604, the wireless chargingsystem 1502 may initialize a cycle counter that is used to control thenumber of power reductions or power reduction cycles performed at eachcharging coil 1504 ₁-1504 _(n).

At block 1606, the wireless charging system 1502 may reduce powertransmitted through a current charging coil 1504 ₁-1504 _(n), and thewireless charging system 1502 may wait for response messages at block1608. The response message may include a request to increase power. Ifat block 1610, the wireless charging system 1502 determines that noresponse message has been received, then at block 1612, the wirelesscharging system 1502 may increase the cycle counter. If at block 1614,the wireless charging system 1502 determines that the maximum number ofcycles has been performed, the process continues at block 1616.Otherwise, the wireless charging system 1502 may initiate a new cycle atblock 1606. If at block 1610, the wireless charging system 1502determined that a response message had been received, the processcontinues at block 1616.

At block 1616, the wireless charging system 1502 may increment the coilcounter to select a next charging coil 1504 ₁-1504 _(n) to receive areduction in power. At block 1618, the wireless charging system 1502 maydetermine that the next selected charging coil 1504 ₁-1504 _(n) and theprocess may return to block 1616. Otherwise, the process returns toblock 1604.

Example of a Processing Circuit

FIG. 17 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1700 that may be incorporated in acharging device or in a receiving device that enables a battery to bewirelessly charged. In some examples, the apparatus 1700 may perform oneor more functions disclosed herein. In accordance with various aspectsof the disclosure, an element, or any portion of an element, or anycombination of elements as disclosed herein may be implemented using aprocessing circuit 1702. The processing circuit 1702 may include one ormore processors 1704 that are controlled by some combination of hardwareand software modules. Examples of processors 1704 includemicroprocessors, microcontrollers, digital signal processors (DSPs),SoCs, ASICs, field programmable gate arrays (FPGAs), programmable logicdevices (PLDs), state machines, sequencers, gated logic, discretehardware circuits, and other suitable hardware configured to perform thevarious functionality described throughout this disclosure. The one ormore processors 1704 may include specialized processors that performspecific functions, and that may be configured, augmented or controlledby one of the software modules 1716. The one or more processors 1704 maybe configured through a combination of software modules 1716 loadedduring initialization, and further configured by loading or unloadingone or more software modules 1716 during operation.

In the illustrated example, the processing circuit 1702 may beimplemented with a bus architecture, represented generally by the bus1710. The bus 1710 may include any number of interconnecting buses andbridges depending on the specific application of the processing circuit1702 and the overall design constraints. The bus 1710 links togethervarious circuits including the one or more processors 1704, and storage1706. Storage 1706 may include memory devices and mass storage devices,and may be referred to herein as computer-readable media and/orprocessor-readable media. The storage 1706 may include transitorystorage media and/or non-transitory storage media.

The bus 1710 may also link various other circuits such as timingsources, timers, peripherals, voltage regulators, and power managementcircuits. A bus interface 1708 may provide an interface between the bus1710 and one or more transceivers 1712. In one example, a transceiver1712 may be provided to enable the apparatus 1700 to communicate with acharging or receiving device in accordance with a standards-definedprotocol. Depending upon the nature of the apparatus 1700, a userinterface 1718 (e.g., keypad, display, speaker, microphone, joystick)may also be provided, and may be communicatively coupled to the bus 1710directly or through the bus interface 1708.

A processor 1704 may be responsible for managing the bus 1710 and forgeneral processing that may include the execution of software stored ina computer-readable medium that may include the storage 1706. In thisrespect, the processing circuit 1702, including the processor 1704, maybe used to implement any of the methods, functions and techniquesdisclosed herein. The storage 1706 may be used for storing data that ismanipulated by the processor 1704 when executing software, and thesoftware may be configured to implement any one of the methods disclosedherein.

One or more processors 1704 in the processing circuit 1702 may executesoftware. Software shall be construed broadly to mean instructions,instruction sets, code, code segments, program code, programs,subprograms, software modules, applications, software applications,software packages, routines, subroutines, objects, executables, threadsof execution, procedures, functions, algorithms, etc., whether referredto as software, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. The software may reside in computer-readableform in the storage 1706 or in an external computer-readable medium. Theexternal computer-readable medium and/or storage 1706 may include anon-transitory computer-readable medium. A non-transitorycomputer-readable medium includes, by way of example, a magnetic storagedevice (e.g., hard disk, floppy disk, magnetic strip), an optical disk(e.g., a compact disc (CD) or a digital versatile disc (DVD)), a smartcard, a flash memory device (e.g., a “flash drive,” a card, a stick, ora key drive), RAM, ROM, a programmable read-only memory (PROM), anerasable PROM (EPROM) including EEPROM, a register, a removable disk,and any other suitable medium for storing software and/or instructionsthat may be accessed and read by a computer. The computer-readablemedium and/or storage 1706 may also include, by way of example, acarrier wave, a transmission line, and any other suitable medium fortransmitting software and/or instructions that may be accessed and readby a computer. Computer-readable medium and/or the storage 1706 mayreside in the processing circuit 1702, in the processor 1704, externalto the processing circuit 1702, or be distributed across multipleentities including the processing circuit 1702. The computer-readablemedium and/or storage 1706 may be embodied in a computer programproduct. By way of example, a computer program product may include acomputer-readable medium in packaging materials. Those skilled in theart will recognize how best to implement the described functionalitypresented throughout this disclosure depending on the particularapplication and the overall design constraints imposed on the overallsystem.

The storage 1706 may maintain software maintained and/or organized inloadable code segments, modules, applications, programs, etc., which maybe referred to herein as software modules 1716. Each of the softwaremodules 1716 may include instructions and data that, when installed orloaded on the processing circuit 1702 and executed by the one or moreprocessors 1704, contribute to a run-time image 1714 that controls theoperation of the one or more processors 1704. When executed, certaininstructions may cause the processing circuit 1702 to perform functionsin accordance with certain methods, algorithms and processes describedherein, including the methods illustrated in FIGS. 7, 16 and 18.

Some of the software modules 1716 may be loaded during initialization ofthe processing circuit 1702, and these software modules 1716 mayconfigure the processing circuit 1702 to enable performance of thevarious functions disclosed herein. For example, some software modules1716 may configure internal devices and/or logic circuits 1722 of theprocessor 1704, and may manage access to external devices such as atransceiver 1712, the bus interface 1708, the user interface 1718,timers, mathematical coprocessors, and so on. The software modules 1716may include a control program and/or an operating system that interactswith interrupt handlers and device drivers, and that controls access tovarious resources provided by the processing circuit 1702. The resourcesmay include memory, processing time, access to a transceiver 1712, theuser interface 1718, and so on.

One or more processors 1704 of the processing circuit 1702 may bemultifunctional, whereby some of the software modules 1716 are loadedand configured to perform different functions or different instances ofthe same function. The one or more processors 1704 may additionally beadapted to manage background tasks initiated in response to inputs fromthe user interface 1718, the transceiver 1712, and device drivers, forexample. To support the performance of multiple functions, the one ormore processors 1704 may be configured to provide a multitaskingenvironment, whereby each of a plurality of functions is implemented asa set of tasks serviced by the one or more processors 1704 as needed ordesired. In one example, the multitasking environment may be implementedusing a timesharing program 1720 that passes control of a processor 1704between different tasks, whereby each task returns control of the one ormore processors 1704 to the timesharing program 1720 upon completion ofany outstanding operations and/or in response to an input such as aninterrupt. When a task has control of the one or more processors 1704,the processing circuit is effectively specialized for the purposesaddressed by the function associated with the controlling task. Thetimesharing program 1720 may include an operating system, a main loopthat transfers control on a round-robin basis, a function that allocatescontrol of the one or more processors 1704 in accordance with aprioritization of the functions, and/or an interrupt driven main loopthat responds to external events by providing control of the one or moreprocessors 1704 to a handling function.

In certain implementations, the apparatus 1700 includes or operates as awireless charging device that has a battery charging power sourcecoupled to one or more charging circuits, a plurality of charging cellsand a controller, which may be included in the one or more processors1704. The plurality of charging cells may be configured to provide acharging surface. At least one coil may be configured to direct anelectromagnetic field through a charge transfer area of each chargingcell while charging a device placed on the charging surface.

In one implementation, the charging device includes a plurality ofcharging circuits, each charging circuit including a transmitting coiland a capacitor coupled at a node, a driver circuit configurable toprovide a charging current to one or more charging circuit in theplurality of charging circuits, and a controller. The controller may beconfigured to cause a first pulse to be transmitted through each of theplurality of charging circuits and to determine peak voltage at each ofthe nodes in the plurality of charging circuits, where the peak voltageat each node is responsive to the first pulse and indicative of acoupling coefficient with a receiving coil in a chargeable device. Thecontroller may be configured to determine that a minimum peak voltageresponsive to the first pulse is associated with a first chargingcircuit in the plurality of charging circuits, and to configure thedriver circuit to provide a first charging current to the first chargingcircuit.

In some implementations, the controller is further configured to detectthat voltage at the node in the first charging circuit exceeds athreshold voltage while providing the first charging current to thefirst charging circuit, cause a second pulse to be transmitted throughone or more other charging circuits in the plurality of chargingcircuits, determine that a minimum peak voltage responsive to the secondpulse is associated with a second charging circuit in the plurality ofcharging circuits, and configure the driver circuit to provide a secondcharging current to the second charging circuit. In some instances, thecontroller may configure the driver circuit to discontinue the firstcharging current when providing the second charging current to thesecond charging circuit. In some instances, the controller may configurethe driver circuit to redirect at least a portion of the first chargingcurrent to the second charging circuit as the second charging current.

In some implementations, the controller may configure the driver circuitto reduce the first charging current after detecting that voltage at thenode in the first charging circuit exceeds a threshold voltage whileproviding the first charging current to the first charging circuit,configure the driver circuit to increase the first charging current whena message requesting power increase is received from the chargeabledevice, and configure the driver circuit to discontinue the firstcharging current when the message requesting power increase is notreceived from the chargeable device. In some examples, the chargingdevice may include an ASK demodulator configured to decode the messagerequesting power increase from a signal received through the firstcharging circuit.

In some implementations, the controller is further configured todetermine that a chargeable device is located proximate to at least onetransmitting coil associated with the plurality of charging circuits.The first pulse may be transmitted responsive to determination ofproximity of the chargeable device. The controller may be furtherconfigured to detect an increase in voltage at the node in the firstcharging circuit while providing the first charging current to the firstcharging circuit, and determine that location of the chargeable devicehas changed when the voltage at the node in the first charging circuitexceeds a threshold voltage.

The storage 1706 may include a processor-readable storage medium thathas instructions stored thereon which, when executed by at least oneprocessor of a charging circuit, cause the charging circuit to transmita first pulse through each of a plurality of charging circuits,determine peak voltage at nodes in the plurality of charging circuits,each node coupling a transmitting coil to a capacitor in one chargingcircuit in the plurality of charging circuits, the peak voltage at eachnode being responsive to the first pulse and indicative of a couplingcoefficient with a receiving coil in a chargeable device, determine thata minimum peak voltage responsive to the first pulse is associated witha first charging circuit in the plurality of charging circuits, andprovide a first charging current to the first charging circuit.

The processor-readable storage medium may include instructions thatcause the charging circuit to detect that voltage at the node in thefirst charging circuit exceeds a threshold voltage while providing thefirst charging current to the first charging circuit, transmit a secondpulse through one or more other charging circuits in the plurality ofcharging circuits, determine that a minimum peak voltage responsive tothe second pulse is associated with a second charging circuit in theplurality of charging circuits, and provide a second charging current tothe second charging circuit. The processor-readable storage medium mayinclude instructions that cause the charging circuit to redirect atleast a portion of the first charging current to the second chargingcircuit as the second charging current.

The processor-readable storage medium may include instructions thatcause the charging circuit to reduce the first charging current afterdetecting that voltage at the node in the first charging circuit exceedsa threshold voltage while providing the first charging current to thefirst charging circuit, increase the first charging current when amessage requesting power increase is received from the chargeabledevice, and discontinue the first charging current when the messagerequesting power increase is not received from the chargeable device.

FIG. 18 is a flowchart 1800 illustrating a method for operating awireless charging device. The method may be performed or managed by acontroller in the wireless charging device. At block 1802, the methodincludes transmitting a first pulse through each of a plurality ofcharging circuits. A driver circuit may be configured to provide thefirst pulses and other such pulses. In one example, the pulses mayinclude a partial cycle of an AC current produced by the driver circuit.In another example, the pulses may include multiple cycle of an ACcurrent produced by the driver circuit. In another example, the pulsesmay be step pulses produced by the driver circuit or another circuit.

At block 1804, the method proceeds by determining peak voltage at nodesin the plurality of charging circuits. Each node may be coupled to ormay couple a transmitting coil to a capacitor in one of the chargingcircuits in the plurality of charging circuits. The voltage measured atthe node may be a tank voltage. The peak voltage measured at each noderesponsive to the first pulse may indicate a coupling coefficient withrespect to a receiving coil in a chargeable device. For example, thecoupling coefficient may characterize the coupling between thetransmitting coil in the charging circuit and a receiving coil in achargeable device.

At block 1806, the method continues by determining which of the measurednodes provides the minimum peak voltage responsive to the first pulse.The minimum peak voltage may be associated with a first charging circuitin the plurality of charging circuits. At block 1808, the methodproceeds by providing a first charging current to the first chargingcircuit. The minimum peak voltage may indicate the best coupling betweena transmitting coil and the receiving coil in the chargeable device. Forexample, the peak voltage at each node may be representative of aleakage inductance of a charging circuit associated with each node.

In certain implementations, the method includes detecting that voltageat the node in the first charging circuit exceeds a threshold voltagewhile providing the first charging current to the first chargingcircuit, transmitting a second pulse through one or more other chargingcircuits in the plurality of charging circuit, determining that aminimum peak voltage responsive to the second pulse is associated with asecond charging circuit in the plurality of charging circuits, andproviding a second charging current to the second charging circuit. Insome implementations, the voltage at the node in the first chargingcircuit is monitored while the first charging current is provided to thefirst charging circuit charging in order to determine when thechargeable device is moved. An increase in the voltage at the node mayindicate movement when the change is sufficiently great. In one example,the method includes discontinuing the first charging current whenproviding the second charging current to the second charging circuit. Inanother example, the method includes redirecting at least a portion ofthe first charging current to the second charging circuit as the secondcharging current.

In certain implementations, the method includes reducing the firstcharging current after detecting that voltage at the node in the firstcharging circuit exceeds a threshold voltage while providing the firstcharging current to the first charging circuit, increasing the firstcharging current when a message requesting power increase is receivedfrom the chargeable device, and discontinuing the first charging currentwhen the message requesting power increase is not received from thechargeable device. In some implementations, the voltage at the node inthe first charging circuit is monitored while the first charging currentis provided to the first charging circuit charging in order to determinewhen the chargeable device is moved. An increase in the voltage at thenode may indicate movement when the change is sufficiently great. Thedecrease in the first charging current may cause the chargeable deviceto detect a drop in power transfer. The chargeable device may thenrequest an increase in power transfer. The method may include decodingthe message from the chargeable device requesting power increase from anamplitude shift keyed signal received through the first chargingcircuit.

In certain implementations, the method includes determining that achargeable device is located proximate to at least one transmitting coilassociated with the plurality of charging circuits, wherein the firstpulse is transmitted responsive to determination of proximity of thechargeable device. The method may include detecting an increase involtage at the node in the first charging circuit while providing thefirst charging current to the first charging circuit, and determiningthat location of the chargeable device has changed when the voltage atthe node in the first charging circuit exceeds a threshold voltage.

obtaining first measurements of peak voltage levels at nodes in theplurality of charging circuits. Each node may couple a charging coil toa capacitor in one of the plurality of charging circuits. At block 1802,the method includes providing a first charging current to a firstcharging circuit selected from the plurality of charging circuits basedon a comparison of the first measurements of peak voltage levels. Insome examples, for each node measured in the plurality of chargingcircuits, peak voltage level is representative of a leakage inductanceassociated with a charging coil of the corresponding charging circuit.

In certain examples, the first charging circuit includes a first nodewith lowest peak voltage level of the nodes in the plurality of chargingcircuits. The method may include receiving one or more messages throughthe first charging circuit while the first charging current is beingprovided to the first charging circuit, obtaining a second measurementof peak voltage level at the first node, and discontinuing the firstcharging current when the second measurement of peak voltage level isgreater than the lowest peak voltage level of the nodes.

In some instances, the method includes determining that a chargeabledevice is proximate to at least one charging coil associated with theplurality of charging circuit. The energy pulse may be transmittedthrough each of the plurality of charging circuits responsive todetermination of proximity of the chargeable device.

In certain examples, the first charging circuit is inductively coupledto a chargeable device and the first charging circuit includes a firstnode with lowest measured peak voltage level in the first measurementsof peak voltage levels. The method may include determining that thechargeable device has been moved while the first charging current isbeing provided to the first charging circuit, obtaining secondmeasurements of peak voltage levels at nodes in one or more chargingcircuits. Each node in the in one or more charging circuits may couple acharging coil to a capacitor in the one or more charging circuits. Themethod may include providing a second charging current to a secondcharging circuit selected from the plurality of charging circuits basedon a comparison of the second measurements of peak voltage levels. Thesecond charging circuit may be different from the first chargingcurrent. Determining that the chargeable device has been moved mayinclude obtaining second measurements of peak voltage levels at thenodes in the plurality of charging circuits, and determining that peakvoltage level at the first node has increased. Providing a secondcharging current may include discontinuing the first charging currentand/or redirecting at least a portion of the first charging current tothe second charging circuit.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for” or, in the case of a method claim, theelement is recited using the phrase “step for.”

What is claimed is:
 1. A method for operating a wireless chargingdevice, comprising: transmitting a first pulse through each of aplurality of charging circuits; determining peak voltage at nodes in theplurality of charging circuits, each node coupling a transmitting coilto a capacitor in one charging circuit in the plurality of chargingcircuits, the peak voltage at each node being responsive to the firstpulse and indicative of a coupling coefficient with a receiving coil ina chargeable device; determining that a minimum peak voltage responsiveto the first pulse is associated with a first charging circuit in theplurality of charging circuits; and providing a first charging currentto the first charging circuit.
 2. The method of claim 1, wherein peakvoltage at each node is representative of a leakage inductance of acorresponding charging circuit.
 3. The method of claim 1, furthercomprising: detecting that voltage at the node in the first chargingcircuit exceeds a threshold voltage while providing the first chargingcurrent to the first charging circuit; transmitting a second pulsethrough one or more other charging circuits in the plurality of chargingcircuits; determining that a minimum peak voltage responsive to thesecond pulse is associated with a second charging circuit in theplurality of charging circuits; and providing a second charging currentto the second charging circuit.
 4. The method of claim 3, furthercomprising: discontinuing the first charging current when providing thesecond charging current to the second charging circuit.
 5. The method ofclaim 3, further comprising: redirecting at least a portion of the firstcharging current to the second charging circuit as the second chargingcurrent.
 6. The method of claim 1, further comprising: reducing thefirst charging current after detecting that voltage at the node in thefirst charging circuit exceeds a threshold voltage while providing thefirst charging current to the first charging circuit; increasing thefirst charging current when a message requesting power increase isreceived from the chargeable device; and discontinuing the firstcharging current when the message requesting power increase is notreceived from the chargeable device.
 7. The method of claim 6, furthercomprising: decoding the message requesting power increase from anamplitude shift keyed signal received through the first chargingcircuit.
 8. The method of claim 1, further comprising: determining thata chargeable device is located proximate to at least one transmittingcoil associated with the plurality of charging circuits, wherein thefirst pulse is transmitted responsive to determination of proximity ofthe chargeable device.
 9. The method of claim 8, further comprising:detecting an increase in voltage at the node in the first chargingcircuit while providing the first charging current to the first chargingcircuit; and determining that location of the chargeable device haschanged when the voltage at the node in the first charging circuitexceeds a threshold voltage.
 10. A charging device, comprising: aplurality of charging circuits, each charging circuit including atransmitting coil and a capacitor coupled at a node; a driver circuitconfigurable to provide a charging current to one or more chargingcircuit in the plurality of charging circuits; and a controllerconfigured to: cause a first pulse to be transmitted through each of theplurality of charging circuits; determine peak voltage at each of thenodes in the plurality of charging circuits, the peak voltage at eachnode being responsive to the first pulse and indicative of a couplingcoefficient with a receiving coil in a chargeable device; determine thata minimum peak voltage responsive to the first pulse is associated witha first charging circuit in the plurality of charging circuits; andconfigure the driver circuit to provide a first charging current to thefirst charging circuit.
 11. The charging device of claim 10, wherein thecontroller is further configured to: detect that voltage at the node inthe first charging circuit exceeds a threshold voltage while providingthe first charging current to the first charging circuit; cause a secondpulse to be transmitted through one or more other charging circuits inthe plurality of charging circuits; determine that a minimum peakvoltage responsive to the second pulse is associated with a secondcharging circuit in the plurality of charging circuits; and configurethe driver circuit to provide a second charging current to the secondcharging circuit.
 12. The charging device of claim 11, wherein thecontroller is further configured to: configure the driver circuit todiscontinue the first charging current when providing the secondcharging current to the second charging circuit.
 13. The charging deviceof claim 11, wherein the controller is further configured to: configurethe driver circuit to redirect at least a portion of the first chargingcurrent to the second charging circuit as the second charging current.14. The charging device of claim 10, wherein the controller is furtherconfigured to: configure the driver circuit to reduce the first chargingcurrent after detecting that voltage at the node in the first chargingcircuit exceeds a threshold voltage while providing the first chargingcurrent to the first charging circuit; configure the driver circuit toincrease the first charging current when a message requesting powerincrease is received from the chargeable device; and configure thedriver circuit to discontinue the first charging current when themessage requesting power increase is not received from the chargeabledevice.
 15. The charging device of claim 14, further comprising: anamplitude shift keying demodulator configured to decode the messagerequesting power increase from a signal received through the firstcharging circuit.
 16. The charging device of claim 10, wherein thecontroller is further configured to: determine that a chargeable deviceis located proximate to at least one transmitting coil associated withthe plurality of charging circuits, wherein the first pulse istransmitted responsive to determination of proximity of the chargeabledevice; detect an increase in voltage at the node in the first chargingcircuit while providing the first charging current to the first chargingcircuit; and determine that location of the chargeable device haschanged when the voltage at the node in the first charging circuitexceeds a threshold voltage.
 17. A processor-readable storage mediumhaving instructions stored thereon which, when executed by at least oneprocessor of a charging circuit, cause the charging circuit to: transmita first pulse through each of a plurality of charging circuits;determine peak voltage at nodes in the plurality of charging circuits,each node coupling a transmitting coil to a capacitor in one chargingcircuit in the plurality of charging circuits, the peak voltage at eachnode being responsive to the first pulse and indicative of a couplingcoefficient with a receiving coil in a chargeable device; determine thata minimum peak voltage responsive to the first pulse is associated witha first charging circuit in the plurality of charging circuits; andprovide a first charging current to the first charging circuit.
 18. Theprocessor-readable storage medium of claim 17, wherein the instructionscause the charging circuit to: detect that voltage at the node in thefirst charging circuit exceeds a threshold voltage while providing thefirst charging current to the first charging circuit; transmit a secondpulse through one or more other charging circuits in the plurality ofcharging circuits; determine that a minimum peak voltage responsive tothe second pulse is associated with a second charging circuit in theplurality of charging circuits; and provide a second charging current tothe second charging circuit.
 19. The processor-readable storage mediumof claim 18, wherein the instructions cause the charging circuit to:redirect at least a portion of the first charging current to the secondcharging circuit as the second charging current.
 20. Theprocessor-readable storage medium of claim 17, wherein the instructionscause the charging circuit to: reduce the first charging current afterdetecting that voltage at the node in the first charging circuit exceedsa threshold voltage while providing the first charging current to thefirst charging circuit; increase the first charging current when amessage requesting power increase is received from the chargeabledevice; and discontinue the first charging current when the messagerequesting power increase is not received from the chargeable device.